This application claims the priority of German patent application no. 199 02 194.5, filed in Germany on Jan. 21, 1999, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a flyer drafting arrangement having a condensing zone, arranged downstream of drafting rollers and bordered by a nipping point, for condensing a drafted fiber strand.
A flyer drafting arrangement is prior art in European published patent 455 190. Here it is disclosed that the drafted fiber strand exiting from the front roller pair of the flyer drafting arrangement is wider than it is high and therefore is laterally bundled in a condensing zone downstream of the flyer drafting rollers, so that the spinning triangle, to which the twist from the flyer spindle is retroactive, becomes narrower. A mechanical sliver condenser is provided in the condensing zone, with a delivery roller pair arranged downstream of the mechanical sliver condenser, and to which the twist from the flyer spindle is retroactive.
It has been shown in practice that such mechanical sliver condensers are not entirely satisfactory and that the condensed fibers spread out again before reaching the nipping point after they have left the sliver condenser. Furthermore, it has been shown that sliver condensers always result in a disimprovement in the evenness of the fiber strand.
It is an object of the present invention to create a condensing zone in which the fiber strand drafted in a flyer drafting arrangement is rounded in a satisfactory way so that the condensing effect is not lost.
This object has been achieved in accordance with the present invention in that a pneumatic condensing device is arranged at the condensing zone.
The present invention is based primarily on the knowledge that a pneumatic condensing device not only laterally bundles the drafted fiber strand, but also that it rolls the outer fibers additionally around the core strand, so that the condensing effect is maintained up to the nipping point. The drafted fiber strand is simultaneously rounded to a great extent, so that the twist applied subsequently by the flyer spindle is more even than is the case with the known mechanical sliver condenser.
The desired improvement attained in the condensing zone, arranged downstream of the flyer drafting rollers, is maintained until the ring spinning machine, at which the flyer roving is now more easily drafted. Due to the more even twist of the flyer roving, the twist in the subsequent ring yarn is also significantly more even.
The condensing zone is particularly simply designed when the condensing device comprises a suction device. The suction device can have a suction slit extending essentially in transport direction of the fiber strand, which suction slit is covered by an air-permeable transporting surface which transports the fiber strand. The width of the suction slit determines to a great extent the condensing effect, while the air-permeable transport surface ensures to a great extent a homogenous effect of the pneumatic condensing.
The condensing effect can be particularly great when the suction slit extends to the nipping point. This effectively prevents the condensed fiber strand from spreading out again before reaching the nipping point.
The transporting surface can have various designs. It is contemplated to form the transport surface by at least one guiding apron or to apply a sieve roller. The air-permeable effective width of the transport surface should be wider than that of the suction slit, which in turn should be wider than the width of the condensed fiber strand.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.